Sliding gate having selectively operable gas line for porous plug

ABSTRACT

An operating mechanism for slidable gates which are used to control flow of liquid from a bottom-pour vessel, and a flowcontrolling method. The mechanism is particularly useful for controlling teeming of liquid steel from a tundish into a continuous-casting mold. Most slidable gates either fully open or fully close the outlet of a vessel. The present invention enables the outlet to be partially open, whereby the stream discharging therefrom can be throttled. The mechanism includes a main drive for pushing gates from a ready position to a slow-motion region under the vessel outlet. The slow-motion region of an orifice gate extends at least from a position in which the vessel outlet is partially open to a position in which it is fully open. An opposed auxiliary drive serves to retard movement of a gate as soon as it reaches the slow-motion region. Thereafter, the main drive pushes an orifice gate slowly annd under close control to any desired teeming position within the slow-motion region. The mechanism also includes an improved arrangement for conducting gases to the nozzle at the vessel outlet to prevent skulls from forming, and an improved attaching mechanism for attaching a pouring tube to its holder.

Shapiand, Jr.

[ Nov. 11, 1975 SLIDING GATE HAVING SELECTIVELY OPERABLE GAS LINE FOR POROUS PLUG Primary Examiner-Robert B. Reeves Assistant Examiner-David A. Scherbel 7 Inventor: E? H Shapland champalgn Atturner, Agent, or Firm-Walter P. Wood [73] Assignee: United States Steel Corporation,

Pittsburgh, Pa. [57] ABSTRACT An operating mechanism for slidable gates which are i [22] Filed 1974 used to control flow of liquid from a bottom-pour ves- [21] Appl. No.: 432,370 Sel. and a flow-controlling method. The mechanism is particularly useful for controlling teeming of liquid Related Apphcanon Data steel from a tundish into a continuous-casting mold. [621 V Divlslo" of No? 337351 March 1, 1973 Most slidable gates either fully open or fully close the 3366-806 outlet of a vessel. The present invention enables the outlet to be partially open, whereby the stream dis- [52] US. Cl; 222/148; 266/34 PP; 266/38 Charging therefrom can be throttled The mechanism [51] 11 11. Cl. B22D 37/00 includes a main drive for pushing gates from a ready [58] Field of Search 1614/ 337'; 266/38 position to a slow-motion region under the vessel out- 266/42" 34 222/148 561; 239/145; let. The slow-motion region of an orifice gate extends V 431/ 328 at least from a position in which the vessel outlet is partially open to a position in which it is fully open. [56] References Clted An opposed auxiliary drive serves to retard movement UNITED STATES PAT N S of a gate as soon as it reaches the slow-motion region. 3.465.810 9/1969 Sylvester 266/34 p Thereafter, th main drive pushes an orifice gate 3581.948 6/ 1971 Detaile 222/148 slowly annd under close control to any desired teem- 3,583.692 6/1971 Urso 266/38 ing position within the slow-motion region. The h- 1684267 1973 AfldYZeJak at 266/38 anism also includes an improved arrangement for con- 2; 5/ 1973 Kutzer 4 4 X ducting gases to the nozzle at the vessel outlet to pre- 3,773.--6 KUIZEI" 2-. /l48 t ull rom forming, and an impro ed attaching FOREIGN PATENTS OR APPLICATIONS mechanism for attaching a pouring tube to its holder. 834,234 5/1960 United Kingdom. 266/34 PP I 1,910,707 3/1969 Germany 164/337 3 9 Drawmg Fgures I xxx 5 247 417 7d e l 1/ .96 /4 14- CZ C "4 -'l7 l6 1 43 ,A 7

9 4 #1(//: I an. I l 92 \\|*fi ,[8 l8- I (*QZEtx -22 btl we 5? 01 69- Q Q Ills! I|-|- ,1) )69 l r, I I I I 2/ 293 M 3 t 1 -27 "Hr/4H 4//////93, 23 2/ v v mr l 6/ G1 III I X I00 i Q0 US. Patent Nov. 11, 1975 Sheet 1 014 3,918,613

US., Paimnfl NOV. 11, 1975 Sheet 2 of4 US. mm Nov. 11, 1975 Sheet 3 of 4 TU/VO/SH HEAD Inches US. Patent Nov. 11, 1975 Sheet 4 0f 4 f1rs= 5 A fu/l "mm/e -B full open FLOW, lbs/min ail rank Baa ir fan/r SLIDING GATE HAVING SELECTIVELY OPERABLE GAS LINE FOR POROUS PLUG This is a division of application Ser. No. 337,252, filed Mar. 1, 1973, now U.S. Pat. No. 3,866,806.

This invention relates to an improved operating mechanism for-slidable gates which are used to control flow of liquid from a bottom pour vessel, and to an improved flow-controlling method.

Although my invention is not thus limited, by operating mechanism is particularly useful when applied to a vessel from which liquid metal is teemed into a receiver therebelow, for example, a tundish from which liquid steel is teemed into a continuous-casting mold. My control method is particularly useful when applied in the corresponding operation. Reference can be made to an earlier patent of James T. Shapland, U.S. Pat. No. 3,353,465, of common ownership for a showing of two forms of slidable gate constructions used heretofore on bottompour vessels, and to a number of later patents, also of common ownership, for showings of modifications and improvements to the construction shown in the first Shapland patent.

FIGS. 1-3 of the Shapland patent show a reciprocating gate, different portions of which form a closed area and an orifice. The closed area is positioned under the vessel outlet to prevent flow of liquid from the vessel, and the orifice is positioned thereunder to permit flow. FIGS. 4-6 of the patent show slide-through gates, wherein each gate is either a blank or an orifice gate. A blank gate is positioned under the vessel outlet to prevent flow, and displaced with an orifice gate to permit flow. With either form, the vessel outlet is either fully open or fully closed. There is no provision for teeming through a partially open outlet, that is, using the gate to throttle the pouring stream. Most other gate-operating mechanisms with which I am familiar have a similar lack of flexibility.

In certain operations, it would be advantageous to throttle a pouring stream. Once example is in continuously casting aluminum-killed steel, where oxygen released from the steel combines with excess aluminum and forms aluminum oxide which deposits around the tundish outlet and gate orifice and restricts flow. If the gate with the orifice could be placed in a throttling position in which the outlet is only partially open at the beginning of a casting operation, the effective opening could be increased gradually as the cast progresses to maintain a constant teeming rate and thus compensate for the oxide build-up. Also the gate might be moved momentarily to a position in which the outlet is fully open to flush away the deposit and then returned to a throttling position.

An object of my invention is to provide an improved gate-operating mechanism and an improved flowcontrolling method which enable me to throttle a stream of liquid as it discharges through the outlet of a bottom-pour vessel.

A further object is to provide an improved gateopening mechanism and an improved flow-controlling method which enable me to move an orifice gate lquickly from a ready position into a slow-motion region under a vessel outlet, and thereafter slowly and under close control in either direction to any desired teeming position within the slow-motion region.

A further object is to provide an improved gateoperating mechanism which enables me to change readily either the blank gate or the orifice gate during the course of a teeming operation.

A further object is to provide a gate'operating mechanism which affords the foregoing advantages and at the same time can be used for positioning a separate pouring tube beneath the gate.

A further object is to provide an improved means for introducing gas to a permeable plug in a blank gate and avoiding any need for connecting pipes or tubes to movable parts, and also affording automatic gas shut off when the vessel outlet is opened to begin teeming.

A further object is to provide an improved means for attaching a pouring tube to a holder which can be used in conjunction with a slidable gate.

In the drawings:

FIG. 1 is a top plan view of my gate-operating mechanism and the mounting plate for attaching the mechanism to a bottom-pour vessel;

FIG. 2 is a side elevational view of a portion ofa bottom-pour vessel with my gate-operating mechanism attached;

FIG. 3 is a longitudinal section on line III-III of FIG. 1;

FIG. 4 is a cross section on line IV-IV of FIG. 2, but showing a blank gate positioned under the vessel outlet;

FIG. 5 is a cross section on line V-V of FIG. 2, but showing a blank gate positioned under the vessel outlet;

FIG. 6 is a bottom plan view of the mounting plate;

FIG. 7 is an exploded perspective view of the pouring tube and its holder illustrating my preferred attaching means;

FIG. 8 is a graph comparing the relation between the flow of metal from a tundish and the head of metal therein with the outlet partially open, and the outlet fully open; and

FIG. 9 is a schematic diagram of the hydraulic and pneumatic circuits embodied in the mechanism.

VESSEL AND MOUNTING PLATE FIGS. 2, 3, 4, and 5 show a portion of a conventional bottom-pour vessel for handling liquid metals, for example, a tundish used to teem metal into a continuouscasting mold. The vessel includes a metal shell 10, a refractory lining 12, and a refractory pouring nozzle 13 extending through the lining and shell and defining the outlet. A mounting plate 14 is fixed to the bottom wall of the vessel surrounding the lower portion of the nozzle. Preferably I interpose a sheet 15 of heat insulating material, such as asbestos mill board, between the bottom wall and the mounting plate. As best shown in FIG. 6, the mounting plate has horizontal passages 16 and 17. The passages 16 communicate with series of nozzles 18 fixed to the underside of the mounting plate for supplying cooling air to the springs embodied in my operating mechanism, hereinafter described. The passage 17 has an outlet port 17a for supplying gas (inert and or oxygen) to the vessel nozzle 13 as also hereinafter described. The mounting plate has a plurality of depending lugs 19 for attaching my operating mechanism to the vessel. The lugs have transverse holes 20.

CONSTRUCTION OF THE GATE OPERATING MECHANISM 1 construct my operating mechanism as an assembly which I can install on the mounting plate 14 or remove therefrom as a unit. The mechanism has a fabricated frame 21 on which I mount the other parts. As best shown in FIG. 2, this frame includes a horizontal plate 22, a continuous flange 23 depending from one side edge of the plate, and vertically spaced upper and lower rails 24 and 25 projecting inwardly from the flange. At its opposite side edge, the plate carries depending flange segments 26, 27, and 28 from which horizontally spaced upper rail segments 29, 30 and 31 respectively project inwardly. Horizontally spaced lower rail segments 32 and 33 project inwardly from the flange segments 26 and 28 respectively. The foregoing parts of the frame are rigidly connected to one another, but preferably the lower rail 25 and rail segments 32 and 33 and the lower portions of the flange 23 and flange segments 26 and 28 can be removed. The purpose of the lower rail and rail segments is to support a pouring-tube holder 34, hereinafter described. When no pouring tube is used, the parts on which it would have been supported are not needed. Plate 22 has vertical holes 35 and horizontal holes 36 communicating with the respective vertical holes. The lugs 19 on the mounting plate 14 match the vertical holes and are received therein. I insert pins 37 through the aligned horizontal holes 20 and 36 in the lugs 19 and plate 22 respectively to hold the operating mechansim on the vessel. As hereinafter explained in detail, the upper rail 24 and rail segments 29, 30 and 31 are adapted to support refractory blank gates 38 and orifice gates 39 for movement along a linear path between a ready position, a slow motion region under the nozzle 13, and a removal position beyond the nozzle.

Plate 22 has a central opening 41 which receives a stationary refractory top plate 42 (FIGS. 3, 4 and 5). The latter has the usual orifice 43, which is aligned with the base of the nozzle 13. Since the refractory plate is exposed directly to liquid metal, it must be replaced frequently. Replacement is simple, since the top plate is accessible when the frame 21 is removed from the mounting plate 14.

I mount a main fluid-pressure cylinder 46 on frame 21 at one end of the path of gate movement, and an auxiliary fluid-pressure cylinder 47 at the other end thereof (FIGS. 1, 2 and 3). The main cylinder 46 contains a reciprocate piston 48 and a piston rod 49, which carries a ram 50 at its free end.'Similarly, the auxiliary cylinder 47 contains a reciprocable piston 51 and a piston rod 52, which carries an opposed second ram 53 at its free end. A hydraulic fluid line 54 and a compressed air line 55 are connected to the back and front ends of the main cylinder 46 respectively. Similarly, a hydraulic fluid line 56 and a compressed air line 57 are connected to back and frontends of the auxiliary cylinder 47.

At opposite sides of the nozzle 13, the frame 21 carries opposed gate-supporting levers 60 and opposed tube-holder-supporting levers 61 which are best shown in FIGS. 4 and 5 respectively. The rails 24 and 25 and rail segments 30 are interrupted to accommodate the levers 60 and 61, while the levers 61 are slotted to accommodate the levers 60 (FIG. 4). The gatesupporting levers 60 are pivotally mounted on crowned washers 62 carried by bolts 63 which depend from flange 23 and flange segment 27 at opposite sides of the gate 38 or 39. The flange 23 and flange segment 27 have vertical bores 64 within which I mount compression springs 65 and plungers 66. The springs act downwardly through the plungers against the outboard ends of levers 60, whereby the inboard ends act upwardly against the gate and thus press the gate firmly against the top plate 42 thereabove. The tube-holder supporting levers 61 are pivotally mounted on crowned washers 67 carried by bolts 68 which depend from flange 23 and flange segment 27 at opposite sides of the tube holder 34. Springs 69, which are similar to springs 65, act downwardly through plungers 70 against the outboard ends of levers 61, whereby the inboard ends act upwardly against the tube holder and then press the tube holder firmly against the gate 38 or 39 thereabove. The bores which receive the springs lie directly under the respective nozzles 18 in the mounting plate 14 to admit cooling air to the springs.

OPERATION OF THE GATE-OPERATING MECHANISM Before filling the vessel with metal or other liquid, I position a blank gate 38 under the stationary top plate 42, where it is supported on the inboard arms of the gate-supporting levers 60. The ram 50, operated by the main cylinder 46, is fully retracted. The back end of the auxiliary cylinder 47 contains hydraulic fluid, whereby the second ram 53 is extended into abutting relation with the end of the blank gate 38. I insert an orifice gate 39 sideways through the space between the upper flange segments 26 and 27 into a ready position, where it rests on the rail 24 and on rail segments 29 and 30. The orifice gate 39 has an orifice 73 of the same diameter as the orifice 43 in the top plate 42. The ends of the gates 38 and 39 approximately abut. 4

When I wish to commence teeming, I introduce hydraulic fluid to the back end of the main cylinder 46 via the line 54. Ram 50 is driven toward the nozzle 13 and thus pushes the orifice gate 39 toward the nozzle and displaces the blank gate 38 from the gate-supporting levers 60 toward a removal position beyond the nozzle. The blank gate acts against ram 53 and pushes the piston 51 into a retracted position within the auxiliary cylinder 47. The back end of the piston 51 carries a cylindrical plug 74 (FIG. 3). The back wall of cylinder 47 has a bore 75, which is adapted to receive plug 74, and with which the hydraulic line 56 communicates. The back wall also has a restricted L-shaped passage 76 which affords the only communication between the interior of the cylinder and the bore 75 when plug 74 is received within the bore. A screw 77, which is threadedly engaged with the cylinder wall, controls the effective cross-sectional area of passage 76. Thus the plug 74, bore 75, and passage 76 form a dashpot. I proportion the parts so that the plug first enters the bore when the orifice gate 39 reaches a slow-motion region in which it is supported on the gate-supporting levers 60 and its orifice 73 is nearing or partially under the nozzle 13. The slow-motion region of an orifice gate extends at least from a position of the gate in which the nozzle is partially open, as shown in FIG. 3, to a position in which the nozzle is fully open. Until the plug enters the bore, hydraulic fluid discharges freely from the auxiliary cylinder, whereby the parts move rapidly until the gate reaches the slow-motion region. As soon as the plug enters the bore, hydraulic fluid can escape from the auxiliary cylinder only via the restricted passage 76, whereupon the parts move slowly and under close control in either direction into any desired teeming position within the slow-motion region.

While the teeming operation takes place, the upper rail segments 30 and 31 support the blank gate 38 in its removal position, and the gate-supporting levers 60 support the orifice gate 39, as already stated. IfI wish to remove the blank gate andreplace it with another, I introduce air under pressure to the front end of the auxiliary cylinder 47 via line 57. Piston 52 is driven into a more retracted position, whereupon I can remove the blank gate sideways through the space between the flange segments 30 and 31, and insert another in its place. If I wish to stop pouring, I introducehydraulic fluid to the back end of the auxiliary cylinder 47 and thus push the blank gate 38 from its removal position back under the orifice 43, slowly at first until plug 74 clears the bore 75 and then rapidly. IfI wish to change orifice gates, I first remove the blank gate by the procedure already described, whereafter I introduce air to the front end of the main cylinder 46 via the. line 55 and thus drive the piston 48 and ram 50 intoa retracted position. I insert a new orifice gate into the ready position and next operate cylinder 46 to push the new gate into the slow-motion region on the gate-supporting levers 60, displacing the old orifice gate into its removal position. Alternatively, I may introduce hydraulic fluid to the back end of the auxiliary cylinder 47 and drive the blank gate back under the nozzle and the old orifice gate back to the ready position, from which I remove it sideways. I can then insert a new orifice gate into the ready position and proceed as originally described.

FIG. 8 is a graphwhich shows the relation between the flow rate and head of steel in a tundish (A) with the gate orifice 73 in aninitial throttling position at the beginning of the slow-motion region, and (B) with the gate orifice in its fully open position. In this instance, the initial throttling position is with the circumference of the gate orifice 73 lying on the center of the orifice 42 in the top plate 41, that is, the effective area of the opening is about 40 percent of the area at the fully open position. The abscissae of the graph represent the flow rate and the ordinates the head. In each instance, the flow rate is directly proportional to the head. With a given size of orifice and a given initial throttling position, I can produce a relation anywhere between the lines (A) and (B) of the graph.

HYDRAULIC AND PNEUMATIC CIRCUITS FIG. 9 is a simplified diagram of the hydraulic and pneumatic circuits embodied in my mechanism. The hydraulic circuit includes a tank 80 which contains hydraulic fluid. A feed line 81 extends from the tank to a pump 82 and thence to an inlet port of a four-way valve 83. A return line 84 extends from an outlet port of the valve back to the tank. The aforementioned hydraulic lines 54 and 56 extend from this valve to the main and auxiliary cylinder 46 and 47 respectively. The pneumatic circuit includes a compressed air tank 85. A feed line 86 extends from tank 85 to an inlet port of another four-way valve 87, which has an exhaust 88. The aforementioned air lines 55 and 57 extend from the latter valve to the main and auxiliary cylinders 46 and 47 respectively. FIG. 9 shows the valves 83 and 87 in their neutral positions. When I wish to introduce hydraulic fluid to cylinder 46 or 47, I shift the movable element of valve 83 left or right respectively. Similarly, I shift the movable element of valve 87 to introduce air to either cylinder. The circuit may include various refinements, not shown, such as filters, heaters, and accumulators.

INTRODUCTION OF GAS TO NOZZLE The blank gate 38 illustrated has a gas-permeable plug 91 which is aligned with orifice 43 when the blank gate is positioned to close the vessel outlet. As known in the art, I introduce gas to the base of nozzle 13 through the permeable plug to prevent skulls from forming and blocking the nozzle. Preferably, I introduce an inert gas, usually argon, to stir the metal in the vessel until a few seconds before I am ready to commence teeming. At that point, I introduce a brief burst of oxygen to burn away any skull which may have formed in the nozzle bore. The inclusion of a permeable plug of course is optional, but when I include it, I

prefer to conduct gas to the plug through a novel arrangement of passages, which are best shown in FIGS.'

1 and 5 and which I shall now describe.

As already mentioned, the mounting plate 14 has a passage 17 and an outlet port 17a. The top plate 42 has ahorizontal passage 92 and inlet and outlet ports 92a andv 92b communicating with this passage and extending through the top and bottom faces respectively. The blank gate 38 has a horizontal passage 93, an inlet port 93a communicating with this passage and extending through the top face, and a circular passage 94 communicating with passage 93 and surrounding the permeable plug 91. When the parts are assembled, the outlet port 17a in the mounting plate and the inlet port 92a in the top plate 42 are aligned. Preferably, I insert a sealing ring 95 between the top plate and mounting plate at the juncture of the outlet and inlet ports. When the blank gate 38 is properly positioned under the nozzle 13, the inlet port 93a in the gate and the outlet port 92b in the top plate are aligned. I connect a gas line 96 to either end of passage 17 in the mounting plate, whereby gas may flow through passages 17, 92, 93 and 94 to the permeable plug 91. The other end of passag 17 of course is plugged.

My novel arrangement of passages eliminates need for connecting a pipe or tube to a movable part of the mechanism to conduct gas to the plug, as has been the practice in the prior art. A further advantage is that the gas is immediately and automatically shut off whenever the blank gate is displaced from. the nozzle. It should be I pointed out that my novel arrangement of passages has general utility in gate-operating mechanisms which em-' body a mounting plate, a top plate, and a permeable plug in the slidable gate. Its use is not confined to the specific mechanism described herein.

' POURING TUBE CONSTRUCTION AND OPERATION If I use pouring tube, I assemble the tube 98 on its aforementioned holder 34. As best shown in FIG. 7, the holder 34 is formed of a flat rectangular refractory block 99 and a metal frame 100 covering the side and end edges and bottom of the block. The frame is fixed to the block with a layer of mortar 101. The underside of the frame has a depending skirt 102 which receives the upper end of tube 98. The skirt has four symmetrically arranged slots 103. The upper portion of the tube whereby the tube is positioned automatically always in the same orientation with respect to the holder when the two parts are assembled. This is an important advantage where the tube has outlets 108 in its side walls, since it assures that these outlets are oriented properly with respect to a continuous casting mold. lf side outlets are not used, groove 105 may be continuous around the tube circumference. When either the holder or tube requires replacement, it can be replaced without replacing the other.

When I install the holder 34 and pouring tube 98 in the mechanism, 1 insert the holder sideways through the space between the lower rail segment 32 and the holder-supporting levers 61, where it is in a ready position resting on the lower rail 25 and rail segment 32. Rams 50 and 53 have depending flanges 109 and 110 respectively adapted to abut opposite ends of holder 34. Initially I operate the main cylinder 46 to extend ram 50 and push the holder into a position in which its orifice 107 is aligned with nozzle 13. Preferably I insert a U-shaped stop 112 through appropriately placed holes in the lower rail 25 to retain the holder and tube exactly in this position. When I replace a tube holder and tube, 1 insert a replacement holder into the ready position the same as before, and operate cylinder 46 to push the replacement holder onto the holdersupporting levers 61, where it displaces the old onto the lower rail 25 and rail segment 33. I can remove the holder sideways through the space between the rail segment 33 and the levers 61.

From the foregoing description, it is seen that my invention affords a simple method and mechanism for operating slidable gates which control flow of liquid from a bottom-pour vessel and for using the orifice gate to throttle the pouring stream. The invention enables gates or pouring tubes to be removed and replaced readily at any time. Another feature is that the pouring tube is removably attached to its holder, yet always properly oriented.

I claim:

1. In a combination which includes a vessel having a nozzle in its bottom wall;

a mounting plate fixed to the bottom wall of the vessel around said nozzle; and

a slidable gate mechanism carried by said mounting plate and including a gate for selectively opening and closing said nozzle and a top plate between said gate and said mounting plate; said gate having a gas permeable plug which is aligned with said nozzle when the gate is positioned to close the nozzle and through which gas may be introduced to the nozzle to keep it clear when closed; an improved means for conducting gas to said plug, said means comprising communicating passages formed in said mounting plate, said top plate and said gate leading to said plug, and a line connected to the passage in said mounting plate for introducing gas thereto; communication between the passages of said top plate and said gate being broken automatically when said gate moves to a position in which said plug is out of alignment with said nozzle. 2. A combination as defined in claim 1 in which: said mounting plate has a passage which extends horizontally from said line and a vertical outlet port from its passage; said top plate has a vertical inlet port aligned with the outlet port of said mounting plate, a passage which extends horizontally from its inlet port, and a vertical outlet port from its passage; and said gate has a vertical inlet port aligned with the outlet port of said top plate when the gate is aligned with said nozzle, a passage which extends horizontally from its inlet port, and a circular passage surrounding said plug and communicating with said last-named horizontally extending passage. 3. In a slidable gate mechanism wherein the gate has a permeable plug through which gas can be introduced to the outlet of a vessel, an improved means for conducting gas to said plug, said means comprising a series of passages through stationary parts of the mechanism and a passage in said gate communicating with said plug and with said first-named passages when said plug is positioned under said outlet, whereby the need is avoided for flexible connectors to conduct gas to said plug and communication between said series of passages and the passage in said gate is broken automatically when said gate moves to a position in which said plug is away from said outlet.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,918,613 Dated November 11, 1975 Inventor(s) Earl P. Shapland, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The inven tor's name is misspelled, "Shapiand" should read Shapland Column 1, line 17, "U.S. Patent No. 3,353,465" should read UQS. Patent No. 3,352,465

line 40, "Once" should read One Column 3, line 43, "reciprocate" should read reciprocable Signed and Sealed this [SEAL] Sixth Day of April1976 Attest.

:UTH. C. M AHSON C. MARSHALL DANN nesting ()fjmer (nmmissiuner nfParenrs and Trademarks 

1. In a combination which includes a vessel having a nozzle in its bottom wall; a mounting plate fixed to the bottom wall of the vessel around said nozzle; and a slidable gate mechanism carried by said mounting plate and including a gate for selectively opening and closing said nozzle and a top plate between said gate and said mounting plate; said gate having a gas permeable plug which is aligned with said nozzle when the gate is positioned to close the nozzle and through which gas may be introduced to the nozzle to keep it clear when closed; an improved means for conducting gas to said plug, said means comprising communicating passages formed in said mounting plate, said top plate and said gate leading to said plug, and a line connected to the passage in said mounting plate for introducing gas thereto; communication between the passages of said top plate and said gate being broken automatically when said gate moves to a position in which said plug is out of alignment with said nozzle.
 2. A combination as defined in claim 1 in which: said mounting plate has a passage which extends horizontally from said line and a vertical outlet port from its passage; said top plate has a vertical inlet port aligned with the outlet port of said mounting plate, a passage which extends horizontally from its inlet port, and a vertical outlet port from its passage; and said gate has a vertical inlet port aligned with the outlet port of said top plate when the gate is aligned with said nozzle, a passage which extends horizontally from its inlet port, and a circular passage surrounding said plug and communicating with said last-named horizontally extending passage.
 3. In a slidable gate mechanism wherein the gate has a permeable plug through which gas can be introduced to the outlet of a vessel, an improved means for conducting gas to said plug, said means comprising a series of passages through stationary parts of the mechanism and a passage in said gate communicating with said plug and with said first-named passages when said plug is positioned under said outlet, whereby the need is avoided for flexible connectors to conduct gas to said plug and communication between said series of passages and the passage in said gate is broken automatically when said gate moves to a position in which said plug is away from said outlet. 